Hydraulic-pressure accumulator



Oct. 28, 1969 SHERTE L L 3,474,830 HYDRAULIC-PRESSURE AccuMuLAToR Filed Dec. 14, 1967 v I :2 Sheets-Sheet 1 9 L50 p 11 I I 60* lqcl 7 2 I I9 r I Q SIEGFRIED HE I- I.\'\'E.\TOR.

ATTORNEY Oct. 28, 1969 v s. HERTELL 3,474,830

7 HYDRAULIC-PRESSURE ACCUMULATOR I 2 Sheets-Sheet 2 Filed Dec. 14, 1967- FIGL3 H 4 12, a f F d r z .v (w i 4\ v w a 4 IO M 5 /M HERTELL INVENTOR.

SIEGFRIED ATTORNEY United States Patent Int. Cl. F161 55/04 US. Cl. 13830 Claims ABSTRACT OF THE DISCLOSURE A hydraulic pressure accumulator whose casings has a mouth into which a cylinder is threaded at its end wall so that the cylinder extends into the casing and receives a bipartite piston whose seal is urged outwardly upon increase in the pressure across the piston which subdivides the easing into hydraulic and gas chambers, respectively. At the end wall of the cylinder, a pair of mutually concave members clamp a flat or annular membrane between them to define gas and hydraulic compartments connected by passages in the end Wall with the gas and liquid chambers of the casing respectively.

My present invention relates to a hydraulic pressure accumulator and, more particularly, to a hydraulic/gas pressure accumulator with a piston-type partition between the gas and liquid compartments.

In hydraulic and hydropneumatic networks, it is a common practice to level pressure and volume surges in the hydraulic line and to damp shock waves transmitted to such line while sustaining a pressure throughout all or a portion of the network by providing a hydropneumatic accumulator in which the hydraulic fluid of the network acts against the gas cushion via an intervening movable wall in the form of a membrane or piston. Such pressure accumulators are frequently connected at the discharge side of a hydraulic pump whose output is pulsating or which has a relatively low volumetric rate of flow to deliver larger quantities of hydraulic fluid to the load of the network when the demand increases suddenly or to eliminate the pulses to which the load would otherwise be subject. As indicated, various hydropneumatic accumulators have been proposed, depending upon the particular requirements. In some cases, it is possible to do away with any membrane or separating wall between the gas and liquid chambers, the accumulator in this case being constituted as a hermetically sealed vessel to which the hydraulic fluid is supplied near the bottom so that the surface of the liquid defines the gas chamber thereabove. In other systems, the membrane is a flexible or semiflexible diaphragm spanning the accumulator and mechanically subdividing it into the gas and liquid chambers. Such arrangements have the advantage that they may be used in any position of the accumulator and that the force transmitted from the liquid to the gas via the diaphragm is applied more or less instantaneously because of the relatively low nurture of the flexible membrane. These systems have, however, the significant disadvantage that the membrane has a limited yieldability and may be incapable of sustaining the wide range of fluctuation in the hydraulic requirement of the network or the pressure applied to the accumulator. In fact, to avoid distension of the membrane beyond its elastic limit, it has been proposed, where flexible diaphragms are used, to provide retaining walls limiting the output or input deflections of the membrane so that its distension cannot exceed the elastic limit. When the diaphragm engages one of these retaining walls, however, it is no longer effective to damp pressure surges, to store higher fluid pressures, etc.

3,474,830 Patented Oct. 28, 1969 In an alternative construction, a rigid wall has been provided between the gas and liquid compartments, generally in the form of a freely floating piston suspended between gas and liquid and in sliding but sealing engagement with walls of the accumulator. Such systems have the significant advantage that they are not aiiected adversely by sudden or excessive pressure surges inasmuch as there is no physical distension of the wall, but merely a movement of the piston within its cylinder. It has been found, however, that piston-type accumulators are not always useful because of the relatively high inertia of the piston. The problem of inertia will 'be readily apparent when it is understood that, on the one hand, the piston must slidably engage a wall of the accumulator to seal the chambers from one another, this seal creating a sliding friction to resist displacement of the piston in either direction. Furthermore, the mass of the piston itself creates a problem of inertia and delay of response to sudden and small fluctuations in the pressure within the accumulator. As a consequence, high frequency hydraulicpressure pulsations, which commonly arise in solenoidcontrolled hydraulic systems, in servomechanisms using hydraulic networks and the like, cannot adequately be absorbed. The problem is increased when, in order to enable the sealing engagement of the piston with an accumulator wall to resist high pressures, the piston is provided with a self-reinforcing seal responsive to elevate pressures. Such systems make use of a bipartite piston which sandwiches between the piston parts an annular seal; the latter is compressed outwardly by the hydraulic pressure on one side and the gas pressure on the other side of the wall formed by the piston. In fact, the piston parts may be domed so as to create the possibility of at least limited outward flexure upon the application of axial fluid force in opposite directions to the piston parts, the latter having radial or frustoconical surfaces which urge the seal outwardly upon such flexure. As the pressure increases, therefore, the frictional resistance to displacement of the piston also increases, thereby making the piston even less responsive to high frequency surges. It is also common in structures of this general type to provide a wedge-like frustoconical configuration to the seal seat and the piston parts so that even axial compression of the relatively movable parts of the piston wedges the seal outwardly.

In order to overcome the disadvantages of the low response time of a piston-type accumulator, it has been proposed also to form the accumulator in a very long thin wall vessel or even to provide a thin wall in the piston to permit the minor and brief fluctuations to eflect extension of'the thin wall while the major fluctuations eventually cause displacement of the piston. These systems are or complicated and inconvenient construction, difficult to maintain and often are incapable of sustaining large pressures or substantial surges.

It is, therefore, the principal object of the present invention to provide a hydraulic-pressure accumulator which responds rapidly to damp pressure surges but yet has the advantages of piston-type accumulators.

Another object of this invention is to provide an improved hydraulic-pressure accumulator of low-cost, simplified construction and increased response to large pressure and volume surges as well as high-frequency pulsations.

Still another object of this invention is to provide a compact pressure accumulator, i.e. an accumulator of limited overall length and weight, which has a relatively long useful life, is capable of absorbing generally large volume surges and yet have good response to high-frequency short-duration pressure peaks.

These objects are attained, in accordance with the present invention, by providing a hydraulic-pressure accumulator whose otherwise closed casing has a mouth at one end into which is fitted a piston-guiding cylinder (which opens toward the closed end of the casing), having an end wall at one extremity and mounted at this extremity in the mouth of the casing; in the end wall of the cylinder, I provide a hollow whose overall volume is a fraction of the volume of the gas and liquid chambers into which the piston subdivides the interior of the casing, the hollow being subdivided in turn by an elastic membrane into liquid and gas compartments which are respectively connected by passages in the cylinder membrane and the end wall with the liquid and gas chambers of the casing interior. Advantageously, these passages are of relatively small cross-section by comparison with the cross-section of the inlet port communicating with the main liquid chamber, the latter being formed between the piston and the end wall of the cylinder member. The cylinder may extend into the casing just short of the closed wall thereof and with an annular clearance to form the gas compartment around the cylinder and ahead of the piston. The passage communicating between the main gas chamber and the auxiliary gas compartment in which the membrane is effected thus may be a bore extending outwardly from the gas compartment to the exterior of the cylinder member at a point beyond the junction of the cylinder member with the casing. This junction may be formed by providing the cylinder member with a boss at the aforementioned extremity and threadedly inserting the boss into the internally threaded mouth of the bottle-shaped casing.

According to a more specific feature of this invention, the hollow, which is subdivided by the membrane into the auxiliary gas and liquid compartments, may have limiting surfaces confronting the membrane and concave in the direction thereof to engage the membrane prior to its distension beyond an elastic limit, these surfaces having circular arc segmental profiles in a plane perpendicular to the membrane. Most advantageous is a spheroidal segmental configuration of these surfaces or walls. The membrane may, according to this invention, be generally planar, in which case it can lie in a plane perpendicular to the axis of the cylinder and to the direction of displacement of the piston; alternatively, ring-shaped cylindrical membranes may be provided. In the latter case, the membrane may be coaxial with the cylinder and may cooperate with annular concavities whose sections conform to circular arc segments in axial planes of the device. In either case, it has been found desirable to provide threaded coupling means to connect a pair of end-wall parts together to clamp a membrane between them. When the membrane is generally flat, one of these parts can be a perforated plate conforming to a spheroidal segment and forming the passages between the liquid auxiliary compartment and main chamber. When a cylindrical sleeveshape membrane is provided, the two parts include a core whose annular peripheral concavity is closed by the membrane which also closes an inwardly open concavity annularly formed on the interior of an outer member. The threaded coupling means may be bolts or mating threads formed on the interfitting parts or member forming the end wall.

The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is an axial cross-sectional view of a hydraulicpressure accumulator according to one embodiment of this invention;

FIG. 2 is a cross-sectional view along the line II-H of FIG. 1;

FIG. 3 is a view similar to FIG. 1 showing another embodiment; and

FIG. 4 is a cross-sectional view along the line IV-IV of FIG. 3.

In FIGS. 1 and 2 of the drawing, I show a hydraulicpressure accumulator which comprises a bottle-shaped casing forming a vessel whose mouth 1a is an axially extending cylindrical sleeve into which a cylinder member 2 is inserted. The cylinder member 2 comprises a boss 2a at one extremity which is threadedly received in the internally threaded mouth 1a of the casing 1 and is sealed with respect to the latter by a ring 9. A cylindrical sleeve 2b of the cylinder member extends from the boss 20: axially inwardly into the vessel and has an open end 20 terminating short of the closed far wall 1b of the casing. An inlet port 3, formed in the end wall 10 of the cylinder member 2, communicates via a passage 3a with the main liquid chamber 5 of the accumulator which is defined between the piston 19 and the end wall 10. Inlet port 3 may be connected into any hydraulic system requiring a pressure accumulator, and attention is directed to the discussion of the use of accumulators in Fluid Power, US. Government Printing Oflice, Washington, DC, 1966. Ahead of the piston 19, a main chamber 11, 11a! is formed in which air or some other gas is pressurizable upon movement of the piston in the direction of arrow A.

The piston 19 is bipartite, i.e. compresses a pair of telescopingly interconnected members 19a and 19b having frustoconical seats 19c between which a seal 19d is received. The piston member 19a may be domed at 19e so as to be urged outwardly by the hydraulic axial pressure upon the piston. Thus, when pressure builds up across the piston, the seal 19d is forced outwardly to increase its sealing engagement with the internal Wall of the cylindrical sleeve 2b.

The end wall 10 of the cylinder member 2 is of twopart construction with a member 10a which is integral and unitary with the cylindrical shell 2b while the other member 6 is a perforated plate. The end wall 10 is formed with a hollow (generally designated 4) which is separated by the member 6 from the main liquid chamber 5 and is subdivided by an elastic membrane 7 into auxiliary compartments 14 and 15 respectively connected to the gas chamber 11, 11a by the passages 13, 13a and with the main liquid chamber 5 via the narrow passages 16 through 18 in plate 6. The hollow 4 is formed by a spheroidally concave recess 10b of member 10 which is closed by the membrane 7 and forms a limiting surface for the latter preventing the extension of the membrane upwardly against this surface beyond the elastic limit of the membrane. Surrounding the recess 10b, there is provided an annular groove 10c in which the peripheral bead 7a of the planar membrane 7 is sealingly received. The hollow 4 is completed by the recess 8 of similar spheroidal configuration whose surface limits extension of the membrane downwardly beyond its elastic limit. The recess 8, which is spanned by the membrane 7, is formed in the plate 6 which also has a peripheral recess 6a snugly retaining the bead 7a when plate 6 is threaded into the socket of member 10a. To this end, member 6 may have a cylindrical periphery provided with a thread 6c.

When the accumulator of FIGS. 1 and 2 is connected in a hydraulic network and a large-volume surge is experienced, the surge applies initially to member 19a of the bipartite piston 19 which, because of the inertia of member 19b of the piston and its frictional engagement with the cylinder 2b, compressed the seal 19d outwardly and increases slightly the frictional resistance to displacement while ensuring a tight fit preventing leakage across the piston. During the pressure buildup instant in advance of movement of the piston under the fluid an auxiliary liquid compartment 15 distends the membrane 7, which lies in a. plane perpendicular to the axis of the cylinder, upwardly to displace gas from compartment 14. Chambers 14 and 15 are dimensioned to ensure that, under the usual operating conditions, before the membrane 7 contacts surface 10b or surface 8, depending upon whether the surge is positive or negative, the piston 19 will overcome its inertia and begin to move. Thus, before the membrane 7 contacts surface 10b, piston 19 begins to move in the direction of arrow A in the usual pressure-storing operation of an accumulator.

In FIGS. 3 and 4, I show a modified construction in which the bottle-shaped casing 40 has a cylindrical mouth 41 into which the threaded end wall 23 of the cylinder member 32 is sealingly fitted. A seal 42 between the end wall 23 and the mouth 41 of this vessel prevents leakage of gas from the main chamber 30, 35 defined within the casing 40 piston-guide cylinder 32. The piston, not shown in FIG. 3, may be identical to the piston 19 illustrated in and described with reference to FIG. 1. The end wall 23 is formed of an outer annular part 23a having an inwardly open concavity 33 whose section, in an axial plane, corresponds to a circular arc segment. The concavity 33 is closed by a cylindrical sleeve-shaped elastic membrane 21 whose beads 21a and 21b are clamped in annular recesses 33a and 33b in the outer member 23a. Annular walls 24a and 24b of the inner end-wall member 24 complete the seal. The other annular concavity 34 is formed peripherally of member 24 and is also of circular section in an axial plane. The concavities 33 and 34 thus form surfaces bowed away from the membrane 21 which defines with these surfaces the annular auxiliary compartments 20 and 29. The latter is connected with the liquid chamber 30 behind the piston via a radial bore 28 while the gas compartment 20 is connected with the main gas chamber 35 via a bore 31 which extends from the compartment 20 just beyond the boss formed by the end wall 23. A port 26 in the end-wall member 23a registers with an axially extending channel 27 which delivers the hydraulic fluid to compartment 30. At its lower end (not shown) the vessel 40 is closed as illustrated in FIG. 1 so that hydraulic-fluid pressure surges delivered at port 26 are applied to the piston and to the membrane 21 as described in connection with FIGS. 1 and 2.

The invention described and illustrated is believed to admit of many modifications within the ability of persons skilled in the art all such modifications being considered within the spirit and scope of the invention.

I claim:

1. A hydraulic-pressure accumulator comprising a casing; Wall means in said casing defining a piston-guide path; a piston received in said casing and sealingly engaging said wall means while being slidably movable along said path and subdividing the interior of said casing into a first and a second fluid chamber respectively receiving a hydraulic fluid and a compressible gas, said piston having a pair of relatively axially movable piston members defining an annular space between them, and an annular seal received in said space and compressible outwardly against said wall means upon application of a pressure differential across said piston, an elastic membrane having a cross-section less than that of said piston and disposed in said casing while defining therein a pair of fluid compartments on opposite sides of said membrane, and means forming re spective passages for said hydraulic fluid between said first chamber and one of said compartments and for said gas between said second chamber and the other of said compartments.

2. A hydraulic-pressure accumulator comprising a casing, wall means in said casing defining a piston-guide path, a piston received in said casing and sealingly engaging said wall means while being slidably movable along said path and subdividing the interior of said casing into a first and a second fluid chamber respectively receiving a hydraulic fluid and a compressible gas, an elastic membrane in said casing defining therein a pair of fluid compartments on opposite sides of said membrane, and means forming respective passages for said hydraulic fluid between said first chamber and one of said compartments and for said gas between said second chamber and the other of said compartments, said casing having a mouth, said wall means being formed as a cylinder having an end wall at one extremity, said cylinder being mounted in said mouth at said one extremity and extending therefrom into the interior of said casing, one of said chambers being formed in said cylinder between said piston and said end wall, said end wall being provided with said membrane and defining therewith said fluid compartment.

3. The accumulator defined in claim 2 wherein said compartments have surfaces confronting said membrane and bowed outwardly therefrom.

4. The accumulator defined in claim 3 wherein said surfaces have the configuration of circular arc segments in planes perpendicular to the membrane.

5. The accumulator defined in claim 4 wherein said surfaces are generally spheroidal segments.

6. The accumulator defined in claim 4 wherein said surfaces are generally annular.

7. The accumulator defined in claim 2 wherein said membrane is generally planar and extends perpendicularly to the direction of displacement of said piston and to the axis of said cylinder.

8. The accumulator defined in claim 2 wherein said membrane is a generally cylindrical sleeve coaxial with said cylinder.

9. The accumulator defined in claim 8 wherein said end wall comprises an annular outer member surrounding said membrane and formed with an inwardly concave annular recess closed by said membrane, an inner member received in said membrane and formed with an outwardly concave annular recess closed by said membrane, and means for securing said members together to clamp said membrane between them.

10. The accumulator defined in claim 2 wherein said end wall is provided with a pair of threadedly connectable members concave toward one another and clamping said membrane between them.

References Cited UNITED STATES PATENTS 2,663,320 12/1953 Snyder 13831 2,752,854 7/1956 Prior et al. 1383l 3,015,345 1/196-2 Michael 13831 3,047,023 7/ 1962 Dick 13831 HERBERT F. ROSS, Primary Examiner 

